Operating an agent email inbox with Drin

Drin is bidirectional: besides sending, a domain can receive email, which Drin parses into conversation threads your agent can read and reply to. This is the foundation for an agent you can email.

1. Enable receiving on a domain

• Turn it on: set_domain_receiving with enabled: true (or PATCH /v1/domains/:id/receiving). Drin returns the MX record(s) to publish.
• Publish the MX record(s) in DNS. Until they propagate, no inbound arrives.
• Verify with get_domain_receiving / GET /v1/domains/:id/receiving.

The domain must already be verified for sending (see drin-email-best-practices) so the agent can also reply.

2. Create an inbox (a receive address)

• create_inbox with { address: "support@acme.com", domainId: "<id>" } (or POST /v1/inboxes). This is the address people email to reach the agent.
• List existing ones with list_inboxes.

3. Read inbound — threads, not raw mailboxes

Inbound and outbound messages are joined into threads.

• list_threads (optionally inboxId) — most-recent-first feed. Each thread has a lastMessageAt and subject.
• get_thread with the thread id — the full conversation, oldest→newest, both directions, including each message's direction, from, to, subject, and status.
• For a single message's full content: get_email (detail/lifecycle), get_email_body (the archived { html, text }), and list_email_attachments (download bytes via the authenticated url).

Two ways to know when new mail arrives:

• Poll: periodically list_threads and diff against the last id/timestamp you processed.
• Webhook (preferred for real-time): register a webhook for the inbound events with create_webhook (drin webhooks create --url <url> --event inbound_received / POST /v1/webhooks); Drin POSTs a signed payload when mail is received, and returns a signingSecret ONCE on creation. Verify the signature (drin.webhooks.verify in the SDK) before trusting it.

4. Decide, then reply in-thread

For each new inbound message:

1. Read the body (get_email_body) and any attachments.
2. Decide what to do (answer, take an action with other tools, escalate).
3. Reply on the thread so the recipient's client keeps the conversation together: reply_email with { messageId: "<inbound id>", text: "...", html: "..." } (or POST /v1/emails/:id/reply). Drin sets In-Reply-To/References and the Re: subject automatically; from defaults to the inbox address and to to the original sender.

Keep a record of which message ids you've already handled so you never reply twice (idempotency). When replying to action requests, pass an idempotencyKey.

5. Test without real email

Use the simulator to exercise the whole receive → thread → (webhook) path safely:

• simulate_inbound with { to: "support@acme.com", from: "Customer <c@example.com>", subject: "Help", text: "..." } (or POST /v1/inbound/simulate). The synthesized message is flagged test_mode (excluded from metrics/billing) but flows through ingest, threads, and any webhooks exactly like a real one — so you can build and verify the agent loop before pointing real DNS at it.

Minimal agent loop (pseudocode)

seen = load_processed_ids()
for thread in list_threads(inboxId):
    convo = get_thread(thread.id)
    for msg in convo.messages where msg.direction == "inbound" and msg.id not in seen:
        body = get_email_body(msg.id)
        action = decide(convo, body)          # your agent's reasoning
        reply_email(messageId=msg.id, text=action.reply, idempotencyKey=msg.id)
        seen.add(msg.id)
save_processed_ids(seen)

Always honor suppressions and never reply to mail you can't authenticate as genuinely inbound (verify webhook signatures).